Radio receiving system



June 11, 1935. 'A. N. GOLDSMITH RADIO RECEIVING SYSTEM Filed Feb. 20, 1 2%;

SENS/T/V/TY CONTROL SENSITIVITY CONTROL fYNAL IUD/0 OUTPUTS OF 8077/ RICE/VIM; ARE COMB/NED.

kECE/VER RECEIVER INVENTOR ALFRED N. GOLDSMITH Jada/141w ORNEY Patented June 11, 1935 1?? UNITED, STATES PATENT OFFICE RADIO RECEIVING SYSTEM Alfred N. Goldsmith, New. York, N. Y., assignor to Radio Corporationof America, a corporation of Delaware Application February 20, 1928, Serial No. 255,608 20 Claims. (01. 25020) This invention relates to the radio signalling Fig. 2 is a schematic view showing the details of art and deals more specifically witha method and one: embodiment of this invention.

system for minimizing the elTects of fading in the Referring in detail to Fig. 1 the principles of the reception of signals. i operation of this system will be explained briefly.

It has been proposed heretofore, in order to Receiver l and receiver 2 each havin i s ow 5.

overcome fading, to place a plurality of separate antenna system are placed at any desirable sigreceivers at different signal receiving points, and nalreceiving poi Which po n s may be sp to combine the outputs of these several receivers by eit r a smal ar e d stan e. o t e into a common output circuit, to which the signal pu ircuit f on f the r i fr qu n mp iindicating mechanism is coupled. By virtue of hers of receiver I is connected the input circuit 1 this arrangement, if a signal is fading t n of a sensitivity control unit I, the output circuit point, and the receiver at that point is therefore of this sensit vitycontrol I being connected to an not picking up the required amount of signal eninput Circuit of e Of the radio frequency ampliergy, one of the other receivers supplements this fi of receiver m the Output circuit 5 deficiency in signal energy and thus uniform f n of the radio f qu a l fi s of signal reception is had. However, in a syste of ceiver 2 is connected to the input circuit of the this kind when the signal is fading mom; of t sensitivity control unit 2; andthe output circuit receivers this receiver still functions to reproduce of Sensitivity Control 2 is Connected 150 input whatever undesirable noises may be present such Circuit of O the radio frequency a p fi s of as atmospherics and other stray disturban e receiver I. The final audio output of receiver I o These disturbances are am lified nd fed t th and receiver Zare then combined and led to the aforementioned commonoutput circuit, even S a d c t n m a mthough the receiver is not contributing useful sig- The Operation of t slystem is as f nal energy to the final output. Let us assume that the signal is being received It is therefore an object of this i ti t with normal strength by the receiver l and very providea system of the ch ra t r described in little signal energy is being-received by receiver 2. which the rece ver, which is not yielding useful Under these conditions the sensitivity control I, signal energy, automatically h it amp1jfic3, which is connected to the input circuit of a radio tion or sensitivity reduced, so that the disturbing frequency amplifier of the receiver 2, serves to S0 3 noises are not amplified and combined to any bias the-grid such radio frequency p fi substantial degree with the useful'signal, to cont at eceiver 2 has its amp Sensitivity fuse thefsame. J 1 materially reduced. This prevents'receiverfirom It is a' urther object of this invention to proamp ifying atmospherics and othe Stray disturbvide a radio receiving system having a, plurality ances when that receiver is not contributing use-, of, separate receivers positioned at diiferent m1 slgnal energy h fin output circultfi 35 points, in which all of the receivers except one d se cohdlhohsi VleW of e fact that have their sensitivityv or amplification reduced, receiver 2 is not mtercephhghuhstahhal amolhlt when that one receiver is functioning properly, of slghal energy, e Sehslhvlty h' h to produce the desired amount of useful signal is cqnnecied h e does y funchonho reduce energy I the amplification or sensitivity of receiver l.

It is a further object of this invention to pro- However, m the event that recelvmg cpndltmns vide a signal receiving system employing apluchatlge i 15 now fading 'f but 18 'ality of separate receivers all of which actuate commg m S at the operatlqn 5 reversed 1 a h h S and the SBIlSltlVltY control 2 functions to reduce acommqn m amsmtmw 1c ys em the amplification or sensitivity of receiver I, thus 5 the overall static level is materially reduced.

. cuttin down the am lification f 1 And finally ltlS an obJect of this invention gendisturgances, which s received Lundeslrab e erally to improve the quality and reliability of a will thus be seen, that by virtue of this Signal recelvlhg hl rangement, a plurality of receivers may be proh a other oblectspf the lhvehtloh W111 vided, allhavingtheir output circuits connected to be read y apparent 150 those skilled in the art a common signal indicating mechanism, in which from the fo low description taken in connecthe operation of a receiver which is not producing tion with the accompany drawing in W useful signal energy is nullified, if another receiver Fig. 1 is a diagrammatic representation of a is operating under normal conditions. system embodying this invention and a 1 In the event that signals are weak on each re-' I grid and plate circuits.

ceiving set, the sensitivity controls I and 2 do not function, and the receivers l and 2, therefore, reproduce with maximum efliciency whatever signal energy they receive. Also, if the received signal is strong at both receivers l and 2, the sensitivity of both receivers is cut down correspondingly, so that there is not produced in the common output circuit more than the amount of energy desired to actuate the indicating mechanism.

Many forms of sensitivity control units are known in the art, and this unit, per se, forms no part of the present invention. The'type of sensitivity control which is preferably used in shown as consisting of a vacuum tube having filament,

To the grid circuit is applied a voltage derived from the incoming carrier wave. In the plate circuitof this tube there is included a fixed resistance. Across this resistance there will appear a voltage drop, which varies in accordance with the strength of the incoming carrier wave. "This voltage drop across the resistance is thenapplied to the gridcircuit of-the receiving set, in the form of a variable grid bias, and such variationsin grid bias cause the sensitivity of the set to be varied, in exact pro portion to the variation of the carrier intensity but in inverse relationship. Thus, for example, when the carrier is strong, a high grid bias is applied to the amplifying tubes of the receiver, resulting in low sensitivity or low amplification; while when the carrier is weak, a small grid bias is applied to-the amplifier tubes, resulting in high sensitivity or amplification.

Referring now in detail to Fig. 2, there is disclosed the details of a system embodying the present invention. Receiving antenna it has coupled to it the'radio frequency amplifier II which is in turn coupled to an amplifying tube l2. Conductor l3, connected to the output cirouit of amplifier I2, impresses the potential variations of the carrier current upon the grid of the tube l i. The blocking condenser I5 is provided to'p'revent the application of direct current voltages on the grid of the tube, [4. In the output circuit of the tube M is connected the resistance l5, and the conductors IT and I8 are connected across the terminals of resistance 16. The oppositeends of the conductors l1 and IB are connected to the filament and grid respectively of the'tube'ZO. This forms the electrical equivalent of connecting the resistance l6 between the filament and grid of the tube 20. It will thus be seen that the voltage variations across 16 are impressed upon the grid of tube 20, and these variations serve as the variable bias mentioned above. The detector may be coupled'to the radio frequency amplifying tube Win a manner well understood in the art and such detector may be followed by any desired number of, audio frequency amplifiers. The amplifier 28 is shown, by way of example, andis coupled to the output circuit of the detector 25. The output circuit of 26 is coupled to the common output circuit as shown in the drawing. .A second receivingantenna 2| suitably positioned is coupled to the radio frequency amplifying tube 22, which is in turn coupled to the radio frequency amplifying .tubelfl. The conductor; 39 is connectedbetween the output circuit of the vacuumtube- 2t! and the grid of the tube 3|. .A

blocking condenser. .is provided in a manner well understood in the art. -In the output circuit of the tube 3 I. is the resistance-33, which resistance isconnected .betweenthe. filament andgrid ofthe radio frequency amplify tube by means of conductors 34 and 35.

The detector 49 is coupled to the radio frequency amplifier 2E] and to this is in turn coupled the audio frequency amplifier 4! having its output circuit connected to the common output as shown in the drawing.

This system operates as follows: I

Assuming the signals to be strong in the antenna Ill, the carrier voltage is impressed upon the grid of the tube l4 through the conductor 13, and this voltage causes a corresponding current toflow in the output circuit of the tube M. The voltage drop across the resistance l6, resulting from the flow of current in the plate circuit of the tube I4, is impressed upon the grid of the tube 20. When the carrier in the output of the tube I2 is strong, the drop across the resistance [6 will be relatively large, and will cause a bias upon the grid of the tube 20, sufficient to reduce the sensitivity of the same, and thus nullify'the action of the receiver 2. In the same way when the signals are strong in the receiver 2, and weak in the receiver l the voltages of the carrier received at 2 are impressed upon the sensitivity control tube 3| which produces corresponding voltage drops across the resistance 33, which voltage drops are applied to the grid of the tube l2 in the nature of a bias sufiicient to cut down the amplification of this tube and thereby to nullify its'action.

It is to be understood that the number of stages of radio frequency amplification and the partiou-, lar types of receiving circuits used is unimportant for the purposes of thepresent invention for the reason that the present invention concerns itself with-one stage of radio frequency amplification. Also, this invention may be applied to a super-1 heterodyne receiver or any'other-well'known type of receiver without departing from the spirit of this invention.

Various other changes will readily suggest themselvesto those skilled in the art, and thisinvention is therefore not to be limited to details of structure or manipulation exceptlas defined in the appended claims.

Having thus described my invention I. claim:

1. 'A radio receiving system comprising, in combination, a first receiver and .a second receiver, means for operatingeach of said receivers atthe same'frequency for simultaneously receivingthe desired signal wave, a sensitivity control unit in circuit with said first receiver for govern-- ing the sensitivity of said second receiver, and a sensitivity control unit in circuit with said second receiver for 'governingthe sensitivity of said first receiver.

2. A radio receiving system comprising in combination, a first receiver having vacuum tube amplifiers, a. second receiver having vacuum tube amplifiers, said amplifiers having input and output circuits,-each of said receiverstoperatlng at the same frequency, and a common tuned circuit operatively and symmetrically coupled, to the amplifiers of both said receivers, a sensitivity con trol vunit connected between the output circuitof only one of the vacuirmtubes ofsaid first receiver and the input circuit of one of the vacuum tubes of said second receiver.

3. A radio receiving system comprising in combination," a first receiver, havingfamplifiers, a .sec-

ond receiver having vacuum tube amplifiers, each of said receivers operating at the same. frequency, a'first sensitivity control unit' having input and output circuits, means connecting the output circuit of one ofthe vacuum tubes of'saidfirst amplifier with'the input circuit of said sensitivity control unit, means connecting the output circult of said sensitivity control unit to the input circuit of one ofthe vacuum tubes'of said second receiver, and a second sensitivity control unit similarly connected between the output of a vacuum'tube of said second receiver and the input of a vacuum tube of said first receiver.

4. A radio receiving system comprising in combination, a first receiver having vacuum tube amplifiers, a second receiver having vacuum tube unit and means connecting the output circuit of said second sensitivity control unit with the input circuit of one of the amplifiers of said first receiver.

5. A radio receiving system comprising, in combination, a first receiver located at one point, a second receiver located at a second point, each of said receivers being tuned to the same wave length, means to govern the operation of said first receiver in accordance with the reception of said second receiver, said means being responsive only to said second receiver, and independent means responsive to only said first receiver to govern the operation of said last mentioned receiver in accordance with the reception of said first receiver.

6. A radio receiving system comprising in combination, a first receiver, a second receiver, said receivers being tuned to the same operating wave length, and a sensitivity control unit having an input and an output circuit, said input circuit being connected only to the output circuit of said first receiver, said output circuit of said unit being connected to said second receiver, and a common translating circuit coupled to and energized by both of said receivers.

'7. A radio receiving system comprising in combination, a first receiver, a second receiver, said receivers being tuned to the sameoperating wave length, a first sensitivity control unit having an input and an output circuit, said input circuit being connected to said first receiver and said output circuit being connected to said second receiver, and a second sensitivity control unit having an input and an output circuit, said output circuit of said second unit being connected. to said first receiver and said input circuit of said second unit being connected to said second receiver.

8. The method of eliminating fadingv in a radio receiving system which comprises, receiving signal energy of identical frequency at a plurality of separate points, utilizing a. portion of said signal energy received at one point to control, before being detected, the reception at another of said points, utilizing a portion of said signal energy received at said last mentioned point to control,

before being detected, the reception at said one point, and combining the received signal energy received at said plurality of points only when said energies simultaneously received at both said points are weak.

9. The method of signalling which includes collecting signal energy of identical frequency at a plurality of geographically separated points, amplifying the energy collected at each point, and utilizing a portion of the energy collected at one of the points for controlling in a predetermined manner, the amplification of the energy collected at another point only when there is an appreciable diiierence in signal strength received at said one point relative to that received at another separated point;

10. The method of signalling which includes collecting signal energy of identical frequency at a plurality of geographicallyseparated points; amplifying the energy collected at each point; utilizing a portion of the energy collected at one point for varying in a predetermined man her the amplification of energy collected at another point; and utilizing a portion of the energy collected at said other point for varying, in similar manner, the amplification of the energy collected at said one point, but not utiliz ing at the same time both said portions of collected energy for the purposes specified.

11. The method of signalling which includes collecting signal energy at a pair of geographically separated points; separately amplifying the separately collected energies; rectifying separately, portions of the separately amplified energies; utilizing a portion of the rectified'energy derived from one collecting point to vary the amplification of energy collected at the other point; and utilizing a portion of the separately rectified energy derived from the other separate collecting point, to control the amplification of energy separately collected at said one point.

12. A diversity receiving system comprising two antennae having different fading characteristics, a transmission path in circuit with each of the antennae, means to control the gain in each path solely in dependence upon the amplitude of the energy in the antenna associated with the other path, in order to magnify the ratio of the signal energies received on said antennae.

13. In a signalling system subject to variable transmission conditions, a plurality of receiver amplifiers each receiving and amplifying the same signal and so related to each other that the received signals vary difierently at the several receiver amplifiers with variations in transmission conditions, a separate detector connected to each receiving amplifier, a utilization circuit, and means cross connecting said detectors and amplifiers to cause the receiver having the maximum output to feed a predetermined amount of energy to said utilization circuit and to reduce the output of another receiver amplifier of said system to said utilization circuit.

14. In a signalling system subject to variable transmission conditions, a plurality of receiver amplifiers each receiving the same signal and so related to each other that the received signals vary diiferently at the several receiver amplifiers with variationsin transmission conditions, a separate detector connected to each receiving amplifier, a utilization circuit, means cross connecting 'said'detectors and receiver amplifiers to automatically cause the receiver amplifier hav' ing the maximum output to feed a predetermined amount of energy to said utilization circuit and to reduce the amount of energy fed from another receiver amplifier having a weaker signal.

15. In a signaling system subject to variable signals vary differently at the several receivers with variations in transmission conditions, a receiving circuit, and means controlled by the received carrier component of a given receiver to connect that receiver to the receiving circuit exclusively of the others.

16. In a signaling system subject to variable transmission conditions, a plurality of receivers 'eachreceiving the same signal and so related to each other that the received signals vary differently at the several receivers with variations in transmission conditions, a receiving circuit, and means associated with said circuit to automatically select the receiver having the maximum signal output.

17. In a signaling system subject to variable transmission conditions, a plurality of receivers each receiving the same signal and so related to each other that the received signals vary differently at the several receivers with variations in transmission conditions, a receiving circuit, and means associated With said circuit to automatically select a receiver whose signal output conforms to a desired requirement.

18. In a signaling system subject to variable transmission conditions, a plurality of receivers each receiving the same signal and so related to each other that the received signals vary difierently at the several receivers with variations in transmission conditions, a signal circuit common to'said receivers, and means responsive to the amplitude of the outputs of said receivers for automatically controlling-the gain of at least one of said receivers to render substantially inoperative said one of said receivers when its output is materially lower than that of another of said receivers.

19. In combination, a plurality of signal receivers, and means for automatically controlling over a continuous range the gain of one of said receivers in response to the amplitude of the signal received in at least one of the other of said signal receivers to render substantially inoperative said one of said receivers when the amplitude of the signal Wave received thereby is materially lower than the amplitude of the signal wave received by said other of said signal receivers.

20. In a signaling system subject to variable transmission conditions, a plurality of receivers each receiving the same signal and so related to each other that the received signals vary differ: ently at the several receivers with variations in transmission conditions, and means for automatically controlling over a continuous range the gain of at least one of said receivers in response to the amplitude of the signal received in at least one of the respective others of said signal receivers to render substantially inoperative said one of said receivers when. the amplitude of the signal wave received thereby is materially lower than the amplitude of the signal received by said one of the respective others of said signal receivers.

, ALFRED N. GOLDSMITH. 

